1. Field of the Invention
The present invention relates to a method for manufacturing thin film magnetic head used in magnetic recording apparatus such as magnetic disk devices or magnetic tape devices.
2. Description of Related Art
Recently, with the progress in magnetic recording technology, the density of magnetic recording medium has become greater and storage capacity has become larger. To cope with this situation, a thin film magnetic head that is manufactured using LSI technology has been used as the magnetic head. FIG. 1 is, for example, a secontional view showing the structure of a thin film magnetic head disclosed in the Japanese Patent Application Laid-Open No. 61-110320 (1986). In the figure, numeral 1 denotes a nonmagnetic substrate made of Al.sub.2 O.sub.3 -TiC or the like, numeral 2 denotes a lower core made of soft magnetic thin film of NiFe, NiCo or other magnetic alloy formed on the substrate by plating, sputtering, vapor deposition or other method, and numeral 3 denotes a gap made of Al.sub.2 O.sub.3, SiO.sub.2 or the like formed by sputtering, vapor deposition or other method. Numerals 4a, 4b denote first and second insulation layers made of inorganic matter such as Al.sub.2 O.sub.3 or SiO.sub.2 formed by vapor deposition or another method, or an organic resin such as resist or polymide hardened by heat, electromagnetic waves or the like, numeral 5 denotes a coil made of Cu or the like formed by plating, sputtering, vapor deposition or other method, numeral 6 denotes an upper core made of NiFe, NiCo or other magnetic alloy formed by plating, sputtering, vapor deposition or another method, and numeral 7 denotes a protective film made of Al.sub.2 O.sub.3, SiO.sub.2 or the like formed by sputtering, vapor deposition or another method.
The recording and regenerating operations performed by the thin film magnetic head will be explained below.
Information is recorded in a magnetic medium by a leakage magnetic flux from the gap 3 at the leading edge of the core. A magnetic flux flows in the lower core 2 and upper core 6 due to the signal current flowing in the coil 5. Information is regenerated by voltage changes at both ends of the coil 5 that are caused by electromagnetic induction. The induction is caused by changes in the magnetic flux flowing in the lower core 1 and upper core 6 that react to the magnetic flux leaking out from the magnetic medium at the gap 3. The soft magnetic thin films of the lower and upper core are intended to effectively converge the signal magnetic flux from the magnetic recording medium to interlink with the coil, and therefore the soft magnetic thin films are required to have high magnetic permeability, excellent frequency characteristics, and faithful response to the signal magnetic flux. Therefore, the soft magnetic thin film is generally provided with uniaxial anisotropy, and it is so designed that the easy magnetization axis may be parallel to the track widthwise direction. In this case, the magnetic domains of the upper core are shaped as shown in FIG. 2(a) (arrow A indicating the track widthwise direction and easy magnetization axis), and the signal magnetic flux is led in a vertical direction relative to the easy magnetization axis, so that high magnetic permeability, excellent frequency characteristic, and faithful signal response may be realized.
Since the thin film magnetic head is composed of sequentially laminating various materials in this way and the NiFe, NiCo or other magnetic alloy used as the magnetic core is generally magnetostrictive, magnetic characteristics of the magnetic core deteriorated due to the countermagnetostrictive effect caused by internal stress, when forming magnetic core film, or external stress, when forming other member film adjacent to the magnetic core. Especially when the effect of stress is great, the shape of the magnetic domain of the magnetic core is disturbed, and irregular noise called wiggle noise, that is attributable to magnetic domain fluctuation, occurs in the regenerated signal from the magnetic head. FIG. 3 shows waveforms of a regenerated signal with wiggle noise (a) and a normally regenerated signal without noise (b). To avoid this problem, efforts have been made to strictly control the composition so as to reduce the magnetostriction of the magnetic core, to zero, to minimize the stress by optimizing the forming conditions of members, or to anneal the soft magnetic thin film. Actually, however, the stress depends on numerous control items, and it is difficult to control by optimizing the film forming conditions.
A conventional attempt to anneal the soft magnetic thin film, is disclosed in the Japanese Patent Application Laid-Open No. 61-95716 (1986). Heat treatment was applied after forming the soft magnetic thin film before forming the protective film. The present inventors attempted to heat the structure at 230.degree. C. in the magnetic field before forming the protective film and after forming the soft magnetic thin film of the upper core. The protective film was formed to complete a magnetic head, and finally it was electrically evaluated, but the wiggle noise as shown in FIG. 3(a) was detected, and it was therefore difficult to reduce the wiggle noise by annealing before forming the protective film.